Capacitive touch sensors are used as a user interface to electronic equipment, e.g., calculators, telephones, cash registers, gasoline pumps, etc. The capacitive touch sensors are activated (controls a signal indicating activation) by a change in capacitance of the capacitive touch sensor when an object, e.g., user finger tip, causes the capacitance thereof to change. Referring to FIG. 1, depicted is a prior technology capacitive touch sensor generally represented by the numeral 100. The prior technology capacitive touch sensor 100 comprises a substrate 102, a sensor element 112 and a protective covering 108, e.g., glass. When a user finger tip 110 comes in close proximity to the sensor element 112, the capacitance value of the sensor element 112 changes. This capacitance change is electronically processed (not shown) so as to generate a signal indicating activation of the capacitive touch sensor 100 by the user (only finger tip 110 thereof shown). The protective covering 108 may be used to protect the sensor element 112 and for marking of the sensor 100.
Problems exist with proper operation of the sensor 100 that may be caused by water, oil, mud, and/or food products, e.g., ketchup and mustard, either false triggering activation or inhibiting a desired activation thereof. Also problems exist when metallic objects (not shown) come in near proximity of the sensor element 112 and cause an undesired activation thereof. When there are a plurality of sensors 100 arranged in a matrix, e.g., numeric and/or pictorial arrangement, activation of an intended one of the sensors 100 may cause a neighbor sensor(s) 100 to undesirably actuate because of the close proximity of the user finger tip 110, or other portion of the user hand (not shown). This multiple activation of more then one sensor 100 may be caused when touching the intended sensor 100 and a portion of the user's hand also is sufficiently close to adjacent neighbor sensors 100 for activation thereof.
Each capacitive touch sensor key or button comprises a capacitive sensor on a substrate, a thin dielectric spacer layer over the capacitive touch sensor, and a deformable metal target layer (e.g., key or button) over the thin dielectric spacer layer. When the deformable metal target layer is depressed, the capacitance value of the capacitive sensor changes (increases). This change in capacitance value is detected and is used to indicate that the key or button has been pressed. A problem exists however in that the deformable metal target layer is light opaque and therefore precludes backlighting thereof. Existing published solutions for capacitive touch sensor designs are mechanically very thin. They rely on simple flat spacer layers less than about 50 micrometers thick and continuous conductive metal sheets for targets that do not allow light to pass therethrough.